A:meant; are
B:meant; had bee
C:have meant; were
D:have meant; are
1____2____3____4=1
1____2____3____4____5____6____7=1
觅食之后,忽然有了兴至,就朝着这片天空叫上几声。____
More historical buildings in the old town will fall down________we try our best to protect them.
在下列四支试管中分别加入一些物质。甲试管:豆浆;乙试管:人体必需的8种氨基酸溶液;丙试管:牛奶和蛋白酶;丁试管:人血液中的红细胞和蒸馏水。上述四支试管中加入双缩脲试剂振荡后,有紫色反应的是 ( )